1. Field of Invention
U.S. Pat. Nos. 4,853,446 and 4,855,424 disclose and claim novel compounds and compositions which have been found to inhibit the build-up of scale on the walls of vinyl chloride polymerization reactors. Such reactor scale interferes with heat transfer, and consumes valuable monomer which is lost to the final products, and results in the increase in waste product that must be disposed of safely.
The above listed patents disclose the use of the additive of the invention in various polymerization reactions for making polyvinyl chloride including emulsion polymerization, bulk or mass polymerization, suspension polymerization and microsuspension polymerization.
Copending application Ser. No. 07/424,435 filed on even date herewith, discloses and claims the use of the compounds and compositions disclosed in the foregoing patents in a microsuspension process wherein the polymerization is conducted in a tubular reaction zone without agitation. The disclosure of this copending application is incorporated herein by reference. The latter microsuspension process is disclosed and claimed in U.S. Pat. Nos. 2,981,722; 4,377,672 and 4,528,327, the disclosures of which are incorporated by reference. In this process, the tubular reactor is preferentially vertically elongated and preferably has a substantially circular cross-section.
The purpose of this invention is to provide improved polyvinyl chloride polymerization processes that utilize certain phenothiazine derivatives to reduce reactor wall fouling or scale deposits, as well as flocculated material during polymerization of vinyl chloride and comonomers.
2. Prior Art
U.S. Pat. No. 2,415,252 describes the preparation of phenothiazine derivatives by reacting phenothiazine with formaldehyde and an alcohol under conditions that produce a modified phenothiazine that has attached thereto a methylene group and an alkoxy group. The compounds and their solutions in oil are said to be useful for pharmaceutical, veterinary and pest-control purposes.
U.S. Pat. No. 2,528,092 describes the reaction of phenothiazine with formaldehyde and N-dimethylaniline. The resulting compound is useful as an antioxidant for mineral oil lubricants.
U.S. Pat. No. 4,465,881 describes N,N'-dimers of phenothiazine or a substituted phenothiazine. The compounds result from the linkage of two phenuchiazine molecules through their N groups. These dimers are prepared by heating phenothiazine in the presence of an organic peroxide. These dimers are disclosed to be useful to stabilize vinyl aromatic compounds such as styrene and substituted styrenes against undesired polymerization.
U.S. Pat. No. 4,529,500 discloses the use of the N,N'-dimer of phenothiazine or a substituted phenothiazine to protect hydrocarbon processing equipment against fouling during the processing of hydrocarbons at elevated temperatures.
An article published in the U.S.S.R. by Romanovich and co-authors and reported in Chemical Abstracts as 98:144251d, describes the reaction of phenothiazine and formaldehyde under conditions that favor the production of hardened products, wherein reaction appears to take place at the nitrogen group of the phenothiazine, ultimately resulting in the formation of cross-linked products of relatively high molecular weight.
In U.S. Pat. No 4,229,510, a polymer material is formed from a substituted phenothiazine wherein the nitrogen group is substituted with an alkyl group. It appears that reaction with formaldehyde occurs between the phenyl groups and formaldehyde. The resulting product has the nitrogen group blocked with the alkyl group of the starting material. The resulting products are reported to have photoconductive properties.
U.S. Pat. No. 4,565,834 describes compounds that have the formula of a dimer or polymer of phenothiazine. The patentees' compositions are useful as stabilizer-containing reactive components for the production of polyurethane foams which have little or no tendency toward core decolorization.